The present invention relates to an operating circuit for a load, in particular a low-pressure discharge lamp.
In this case, the invention is based on an oscillator circuit for high-frequency operation of the load, in which case the circuit is supplied with a voltage with a dominant DC element. Specifically, a free-running oscillator circuit is considered, in which a bipolar transistor bridge is driven by means of a switching control device such that the process of switching the bipolar transistors on and off allows the potential of a bridge tap to oscillate at the operating frequency. To do this, with free-running oscillator circuits, the load current is fed back through the switching control device in order to switch and control the bipolar transistors.
A major problem in the design and--with regard to the tolerances--in the production of such a circuit is to consider three functional criteria simultaneously, namely radio suppression, relief of the transistor switching load and minimizing switching losses, and, finally, the power which is passed to the load. The relationship between these three criteria in conventional circuits is highly complex. Taking account of all three aspects at the same time is feasible either only on the basis of a very complex circuit design and with correspondingly tight tolerances with regard to the various electrical variables and operating parameters, or frequently cannot be achieved at all in a satisfactory manner.